Epilepsy describes a condition in which a person has recurrent seizures due to a chronic, underlying process. Epilepsy refers to a clinical phenomenon rather than a single disease entity, since there are many forms and causes of epilepsy. Using a definition of epilepsy as two or more unprovoked seizures, the incidence of epilepsy is estimated at approximately 0.3 to 0.5 percent in different populations throughout the world, with the prevalence of epilepsy estimated at 5 to 10 people per 1000.
An essential step in the evaluation and management of a patient with a seizure is to determine the type of seizure that has occurred. The main characteristic that distinguishes the different categories of seizures is whether the seizure activity is partial (synonymous with focal) or generalized.
Partial seizures are those in which the seizure activity is restricted to discrete areas of the cerebral cortex. If consciousness is fully preserved during the seizure, the clinical manifestations are considered relatively simple and the seizure is termed a simple-partial seizure. If consciousness is impaired, the seizure is termed a complex-partial seizure. An important additional subgroup comprises those seizures that begin as partial seizures and then spread diffusely throughout the cortex, which are known as partial seizures with secondary generalization.
Generalized seizures involve diffuse regions of the brain simultaneously in a bilaterally symmetric fashion. Absence or petit mal seizures are characterized by sudden, brief lapses of consciousness without loss of postural control. Atypical absence seizures typically include a longer duration in the lapse of consciousness, less abrupt onset and cessation, and more obvious motor signs that may include focal or lateralizing features. Generalized tonic-clonic or grand mal seizures, the main type of generalized seizures, are characterized by abrupt onset, without warning. The initial phase of the seizure is usually tonic contraction of muscles, impaired respiration, a marked enhancement of sympathetic tone leading to increased heart rate, blood pressure, and pupillary size. After 10-20 s, the tonic phase of the seizure typically evolves into the clonic phase, produced by the superimposition of periods of muscle relaxation on the tonic muscle contraction. The periods of relaxation progressively increase until the end of the ictal phase, which usually lasts no more than 1 min. The postictal phase is characterized by unresponsiveness, muscular flaccidity, and excessive salivation that can cause stridorous breathing and partial airway obstruction. Atonic seizures are characterized by sudden loss of postural muscle tone lasting 1-2 s. Consciousness is briefly impaired, but there is usually no postictal confusion. Myoclonic seizures are characterized by a sudden and brief muscle contraction that may involve one part of the body or the entire body.
The synaptic vesicle protein 2A (“SV2A”) has been identified as a broad spectrum anticonvulsant target in models of partial and generalized epilepsy. Studies performed in animal models and human tissue suggest that changes in the expression of SV2A are implicated in epilepsy (for a review see for instance: (a) Mendoza-Torreblanca et al. “Synaptic vesicle protein 2A: basic facts and role in synaptic function” European Journal of Neuroscience 2013, pp. 1-11; (b) Kaminski R M, et al. “Targeting SV2A for Discovery of Antiepileptic Drugs”. In: Noebels J L, Avoli M, Rogawski M A, et al., editors. Jasper's Basic Mechanisms of the Epilepsies [Internet]. 4th edition. Bethesda (Md.): National Center for Biotechnology Information (US); 2012. Available from: http://www.ncbi.nlm.nih.gov/books/NBK98183/).
The exact role of SV2A remains unclear but studies suggest that changes in the expression of SV2A affect synaptic function (Nowack et al. “Levetiracetam reverses synaptic deficits produced by overexpression of SV2A” PLoS One 2011, Volume 6 (12), e29560). It has also been suggested that SV2A is a key player in exocytosis and is involved in neurotransmission (Crowder et al. “Abnormal neurotransmission in mice lacking synaptic vesicle protein 2A (SV2A)” Proc Nat Acad Sci USA 1999, 96, pp. 15268-15273) and studies in knock-out mice suggest that lack of SV2A results in an imbalance between glutamatergic and GABAergic neurotransmission (Venkatesan et al. “Altered balance between excitatory and inhibitory inputs onto CA pyramidal neurons from SV2A-deficient but not SV2B-deficient mice” J Neurosci Res 2012, 90, pp. 2317-2327). Decreased expression of SV2A may be a consequence of seizure activity and may be involved in the progression of epilepsy (van Vliet et al. “Decreased expression of synaptic vesicle protein 2A, the binding site for levetiracetam, during epileptogenesis and chronic epilepsy” Epilepsia 2009, 50, pp. 422-433; Feng et al. “Down-regulation of synaptic vesicle protein 2A in the anterior temporal neocortex of patients with intractable epilepsy” J Mol Neurosci 2009, 39, pp. 354-359; Toering et al. “Expression patterns of synaptic vesicle protein 2A in focal cortical dysplasia and TSC-cortical tubers” Epilepsia 2009, 50, pp. 1409-1418) and epileptogenesis in patients with brain tumours (de Groot et al. “Expression of synaptic vesicle protein 2A in epilepsy-associated brain tumors and in the peritumoral cortex” Neuro-Oncology 2010, 12, pp. 265-273).
SV2A ligands include levetiracetam (Lynch et al. “The synaptic vesicle protein SV2A is the binding site for the antiepileptic drug levetiracetam” Proc. Natl. Acad. Sci. USA 2004, Vol. 101, pp. 9861-9866), brivaracetam and seletracetam (Kaminski R M, et al. “Targeting SV2A for Discovery of Antiepileptic Drugs”. In: Noebels J L, Avoli M, Rogawski M A, et al., editors. Jasper's Basic Mechanisms of the Epilepsies [Internet]. 4th edition. Bethesda (Md.): National Center for Biotechnology Information (US); 2012. Available from: http://www.ncbi.nlm.nih.gov/books/NBK98183/; Nowack et al. “Levetiracetam reverses synaptic deficits produced by overexpression of SV2A” PLoSone December 2011, Vol. 6(12), e29560).
Levetiracetam, (−)-(S)-α-ethyl-2-oxo-1-pyrrolidine acetamide or (S)-2-(2-oxopyrrolidin-1-yl)butanamide,
is an antiepileptic drug. It showed no activity in traditional acute models (maximal electroshock and pentylenetetrazol seizure tests) but was found potent in chronic epilepsy models and in genetic models of generalized epilepsy. It has shown a high safety margin compared to other antiepileptic drugs (Klitgaard “Levetiracetam: the preclinical profile of a new class of antiepileptic drugs” Epilepsia 2001, 42 (Supplement 4), pp. 13-18). It is commercialized under the trademark Keppra®, available as tablets, as an oral solution, and as a concentrate made up into a solution for infusion. Keppra® has been approved in Europe as a monotherapy in patients from 16 years of age with newly diagnosed epilepsy, in the treatment of partial-onset seizures (fits) with or without secondary generalization and as an add-on therapy for use with other anti-epileptic drugs in the treatment of partial-onset seizures with or without generalization in patients from 1 month of age; myoclonic seizures in patients from 12 years of age with juvenile myoclonic epilepsy; and primary generalized tonic-clonic seizures in patients from 12 years of age with idiopathic generalized epilepsy (www.ema.europa.eu). Keppra® has also been approved in the USA as an add-on therapy for the treatment of partial onset seizures in patients from 1 month of age; myoclonic seizures in patients 12 years of age and older with juvenile myoclonic epilepsy; and primary generalized tonic-clonic seizures in patients 6 years of age and older with idiopathic generalized epilepsy. Keppra XR®, available as extended-release tablets, has been approved in the USA for the add-on treatment of partial onset seizures in patients 16 years of age and older with epilepsy (http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm).
Brivaracetam, the 4-n-propyl analog of levetiracetam, (2S)-2-[(4R)-oxo-4-propyl-pyrrolidin-1-yl]butanamide,
is in clinical trials and investigated as monotherapy in partial onset seizures and post-herpetic neuralgia and as add-on therapy in refractory partial onset seizures, Unverricht-Lundborg disease in adolescents and adults and in photosensitive epilepsy (www.clinicaltrials.gov).
Seletracetam, (2S)-2-[(4S)-4-(2,2,-difluorovinyl)-2-oxo-pyrrolidin-1-yl]butanamide,
has been tested in clinical trials.
Processes for the preparation of the three compounds are known in the literature. For instance, processes for making Levetiracetam are disclosed for instance, in EP 0 162 036 and in GB 2 225 322. A process for the preparation of Brivaracetam is disclosed for instance in WO 01/62726. A process for the preparation of Seletracetam is known for instance from WO2005/121082. Alternative processes for making the three compounds are disclosed in EP1806339.
Antiepileptic drugs have found usefulness in neurological and psychiatric disorders, including neuropathic pain, migraine, essential tremor and in anxiety, schizophrenia and bipolar disorder (Landmarck “Antiepileptic drugs in non-epilepsy disorders. Relations between mechanisms of action and clinical efficacy” CNS Drugs 2008, Vol. 22(1), pp. 27-47; Calabresi et al. “Antiepileptic drugs in migraine: from clinical aspects to cellular mechanisms” Trends in Pharmacological Sciences 2007, Vol. 28(4), pp. 188-195; Rogawski and Löscher “The neurobiology of antiepileptic drugs for the treatment of nonepileptic conditions” Nat Med 2004, Vol. 10, pp. 685-692).
Levetiracetam has been found effective or potentially effective in a wide-spectrum of neuropsychiatric disorders including mood disorders (Muralidharan and Bhagwagar “Potential of levetiracetam in mood disorders: a preliminary review” CNS Drugs 2006, Vol. 20, pp. 969-979; Mula et al. “The role of anticonvulsant drugs in anxiety disorders: a critical review of the evidence” J Clin Pshycopharmacol 2007, Vol. 27, pp. 263-272), anxiety disorders (Kinrys et al. “Levetiracetam as adjunctive therapy for refractory anxiety disorders” J Clin Psychiatry 2007, Vol. 68, pp. 1010-1013; Zhang et al. “Levetiracetam in social phobia: a placebo controlled pilot study” J Psychopharmacol 2005, Vol. 19, pp. 551-553; Kinrys et al. “Levetiracetam for treatment-refractory posttraumatic stress disorder” J Clin Psychiatry 2006, Vol. 67, pp. 211-214), pain (Enggaard et al. “Specific effect of levetiracetam in experimental human pain models” Eur J Pain 2006, Vol. 10, pp. 193-198; Dunteman “Levetiracetam as an adjunctive analgesic in neoplastic plexopathies: case series and commentary” J Pain Palliative Care Pharmacother 2005, Vol. 19, pp. 35-43; Price “Levetiracetam in the treatment of neuropathic pain: three case studies” Clin J Pain 2004, Vol. 20, pp. 33-36), movement disorders (Bushara et al. “The effect of levetiracetam on essential tremor” Neurology 2005, Vol. 64, pp. 1078-1080; McGavin et al “Levetiracetam as a treatment for tardive dyskinesia: a case report” Neurology 2003, Vol. 61, pp. 419; Woods et al. “Effects of levetiracetam on tardive dyskinesia: a randomized, double-blind, placebo-controlled study” J Clin Psychiatry 2008, Vol. 69, pp. 546-554; Zivkovic et al. “Treatment of tardive dyskinesia with levetiracetam in a transplant patient” Acta Neurol Scand 2008, Vol. 117, pp. 351-353; Striano et al. “Dramatic response to levetiracetam in post-ischaemic Holmes' tremor” J Neurol Neurosurg Psychiatry 2007, Vol. 78, pp. 438-439) and it is suspected to show potentially beneficial effects in cognitive functioning (Piazzini et al. “Levetiracetam: An improvement of attention and of oral fluency in patients with partial epilepsy” Epilepsy Research 2006, Vol. 68, pp. 181-188; de Groot et al. “Levetiracetam improves verbal memory in high-grade glioma patients” Neuro-oncology 2013, Vol. 15(2), pp. 216-223; Bakker et al. “Reduction of hippocampal hyperactivity improves cognition in amnestic mild cognitive impairment” Neuron 2012, Vol. 74, pp. 467-474; for a review: Eddy et al. “The cognitive impact of antiepileptic drugs” Ther Adv Neurol Disord 2011, Vol. 4(6), pp. 385-407 and references cited therein; Wheless “Levetiracetam in the treatment of childhood epilepsy” Neuropsychiatric Disease and Treatment 2007, Vol. 3(4), pp. 409-421), and behavioral symptoms in dementia (Dolder and Nealy “The efficacy and safety of newer anticonvulsants in patients with dementia” Drugs Aging 2012, Vol. 29(8), pp. 627-637). Animal data and some preliminary clinical trials suggest that levetiracetam may have potential for restraining post-traumatic epilepsy, such as those caused by status epilepticus, traumatic brain injury and ischemic stroke, and it appears to have neuroprotective effects. The potential of levetiracetam in easing epileptogenesis or cognitive dysfunction remains to be ascertained by conclusive animal and clinical studies (for reviews: Löscher and Brandt “Prevention or modification of epileptogenesis after brain insults: experimental approaches and translational research” Pharmacol Rev 2010, Vol. 62, 668-700; Shetty “Prospects of levetiracetam as a neuroprotective drug against status epilepticus, traumatic brain injury and stroke” Front. Neur. 2013, 4:172. Doi: 10.3389/fneur.2013.00172) as it has displayed antiepileptogenic activity in the kindling model in mice and rats. It has also been suggested that levetiracetam inhibits glutamate release (Lee et al. “Levetiracetam inhibits glutamate transmission through presynaptic P/Q-type calcium channels on the granule cells of the dentate gyrus” British Journal of Pharmacology 2009, Vol. 158, pp. 1753-1762).
Seletracetam and Brivaracetam, have been found to reduce the severity of dystonia in the dtsz mutant hamster model and may be helpful in some patients suffering from dyskinetic and dystonic movement disorders (Hamann et al. “Brivaracetam and seletracetam, two new SV2A ligands, improve paroxysmal dystonia in the dtsz mutant hamster” European Journal of Pharmacology 2008, Vol. 601, pp. 99-102).
Positive allosteric modulators of mGluR2 have emerged recently as promising novel therapeutic approaches for the treatment of several CNS disorders, including epilepsy, and some mGluR2 PAMs are currently undergoing clinical trials for the treatment of schizophrenia, and anxiety-depression (www.clinicaltrials.gov, see for instance: JNJ-40411813/ADX71149 by Addex Therapeutics and Janssen Pharmaceuticals, Inc.). The initial suggestion that drugs that dampen glutamatergic transmission may be efficacious in the treatment of epilepsy came from acute non-clinical studies with mixed mGlu2/3 receptor agonists (Moldrich et al. “Glutamate metabotropic receptors as targets for drug therapy in epilepsy” Eur J Pharmacol. 2003, Vol. 476, pp. 3-16). LY379268 and LY389795, two mGlu2/3 receptor agonists, were found ineffective in blocking MES seizures up to doses producing motor impairment but were found effective in the 6 Hz model in a dose-dependent manner (Barton et al. “Comparison of the effect of glutamate receptor modulators in the 6 Hz and maximal electroshock seizure models” Epilepsy Research 2003, Vol. 56, pp. 17-26). Continued administration of an mGlu2/3 agonist paradoxically induced seizure activity in long-term toxicology studies (Dunayevich et al. “Efficacy and tolerability of an mGlu2/3 agonist in the treatment of generalized anxiety disorder” Neuropsychopharmacology. 2008, Vol. 33(7), pp. 1603-10). This paradoxical effect may be related to agonist-induced changes in the sensitivity of the receptor system (tachyphylaxis), but has not been reported however in preclinical models of epilepsy. Positive allosteric modulators, in contrast, modulate ongoing neurotransmission but are not directly stimulatory, thereby reducing the risk for tachyphylaxis.
Prior to seizure activity, increases in extracellular glutamate are measured in human hippocampus and the increase is sustained during epileptogenic activity (During and Spencer “Extracellular hippocampal glutamate and spontaneous seizure in the conscious human brain” Lancet 1993, Vol. 341(8861), pp. 1607-10), thus lending support to the idea that a reduction in glutamate levels may be of benefit in the treatment of epilepsy. In fact, during seizure activity glutamate levels increase to potentially neurotoxic levels. Seizure activity results in progressive structural damage in human brain inducing further abnormalities in glutamate metabolism (Petroff et al. “Glutamate-glutamine cycling in the epileptic human hippocampus” Epilepsia 2002, Vol. 43(7), pp. 703-10). Thus, an mGluR2 positive allosteric modulator or an mGluR2 orthosteric agonist may be expected to protect against seizure-induced neuronal damage.
WO2009/033704 and WO2010/130424 disclose mGluR2 positive allosteric modulators, uses thereof and processes for synthesizing the compounds. WO1997/18199 and WO2003/104217 disclose excitatory amino acid receptor modulator compounds that later were shown to have mGlu2/3 orthosteric agonist activity (see for example Rorick-Kehn et al. (2007) The Journal of Pharmacology and Experimental therapeutics Vol. 321, No. 1, pp. 308-317), further scientific and patent literature disclose additional examples of compounds having mGlu2/3 orthosteric agonist activity, and WO2008/150233 discloses compounds with mGluR2 allosteric activator activity.
Currently available anti-epileptic drugs do not solely affect glutamatergic transmission. Their mechanism of action is generally conceptualized as altering the balance between excitatory (glutamate-mediated) and inhibitory (GABA-mediated) transmission (Johannessen Landmark “Antiepileptic drugs in non-epilepsy disorders: relations between mechanisms of action and clinical efficacy” CNS Drugs 2008, Vol. 22(1), pp. 27-47).
A significant limiting factor in the use of SV2A ligands is tolerability and side-effect profile. For example the effective dose of levetiracetam for partial onset seizures is dosed at 1000 mg, 2000 mg, and 3000 mg, given as twice-daily. The side effects reported for levetiracetam include aggressive or angry behavior, anxiety, change in personality, chills, cough or hoarseness, crying, depersonalization, diarrhea, dry mouth, euphoria, fever, general feeling of discomfort or illness, headache, hyperventilation, irregular heartbeats, irritability, joint pain, loss of appetite, lower back or side pain, mental depression, muscle aches and pains, nausea, painful or difficult urination, paranoia, quick to react or overreact emotionally, rapidly changing moods, restlessness, shaking, shivering, shortness of breath, sleepiness or unusual drowsiness, sore throat, stuffy or runny nose, sweating, trouble sleeping, unusual tiredness or weakness and vomiting. Thus, there is still a need to provide an effective treatment with a lower effective dose of levetiracetam and a more favourable side effect profile for the treatment of epilepsy and related disorders, not only in the adult but also in the pediatric population.